Creep behaviour of cast TiAl based intermetallics

ISSN： 1743-2847

Source： Materials Science and Technology, Vol.11, Iss.11, 1995-11, pp. : 1147-1155

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Abstract

Constant load tensile creep tests were carried out on the cast TiAl based intermetallics Ti–47 Al–2Mn, Ti–47 Al–2Zr, and Ti–48Al (at.-%), prepared by plasma arc melting. Two microstructural conditions dependent on heat treatment were evaluated as follows: a fully lamellar (FL) scheme consisting of a fully transformed coarse lamellar structure with α₂ laths plus γ laths within the grain interiors; and a duplex scheme consisting of fine equiaxed grains of γ with α₂/γ lamellae. The steady state creep behaviour of both microstructural conditions, for each composition, was studied under stresses of 70–300 MN m⁻² in the temperature range 700–900°C. The microstructure was found to have a pronounced influence on the creep resistance. The FL microstructure exhibited superior creep resistance to the duplex microstructure. At temperatures and stress levels at which direct comparisons can be made, the steady state creep rates of the FL structures are an order of magnitude lower than those of the duplex structure. The apparent creep activation energies and stress exponents were measured for both microstructural conditions for each composition. The temperature and stress dependence of the steady state creep rate of both microstructures can be described by the power law creep equation, suggesting dislocation motion as the operative deformation mechanism.MST/1962